The effects of Fe(III) and Fe(II) on anammox process and the Fe-N metabolism

This study aims to compare the effects of different Fe stress on anammox (anaerobic ammonium oxidation) process, therefore seven identical reactors were operated under different Fe(II)/Fe(III) concentrations. After 38 days of operation, the anammox activity was highest (10.49 +/- 0.41 mg-TN/(g-VSS.h)) under conditions of 5 mg/ L-Fe(II), while under 30 mg/L-Fe(III) displayed severe inhibition. The results showed that continuous addition of 30 mg/L-Fe(III) would damage the composition of EPS (extracellular polymeric substances) and make anammox bacteria more sensitive to environmental stress. While high Fe(II) concentrations could result in precipitates encasing granular sludge, affecting substrate utilization. Moreover, the results of Delta NO3- -N/Delta NH4+-N indicated that Fe(II)-dependent nitrate reduction was induced in reactors added with Fe(II). OM27_clade and norank_f__Burkholderiaceae might be candidates for this process according to the correlation of genera and functional genes (based on the PICRUSt 2 functional prediction). Overall, this research is expected to provide new ideas to the effects of Fe(II)/Fe(III) on anammox and to the practical application of coupled system based on anammox in wastewater treatment.

Automated summary

This study compared the effects of different Fe stress on anammox process, finding that high Fe(II) concentrations may lead to precipitate formation while continuous addition of 30 mg/L-Fe(III) can damage EPS composition. Moreover, addition of Fe(II) could induce nitrate reduction, and OM27_clade and norank_f__Burkholderiaceae may play important roles in this process.